NAOSITE: Nagasaki University's Academic Output SITE Title Controlled fabrication of ion track nanowires and channels Spohr, Reimar; Zet, Cristian; Eberhard Fischer, Bernd; Kiesewetter, Helge; Author(s) Apel, Pavel; Gunko, Igor; Ohgai, Takeshi; Westerberg, Lars Nuclear Instruments and Methods in Physics Research Section B: Beam Citation Interactions with Materials and Atoms, 268(6), pp.676-686; 2010 Issue Date 2010-03-15 URL http://hdl.handle.net/10069/32233 Right © 2010 Elsevier B.V. All rights reserved. This document is downloaded at: 2020-09-18T13:32:01Z http://naosite.lb.nagasaki-u.ac.jp Controlled fabrication of … 1 9-Dec-09 1 2 Controlled fabrication of ion track nanowires and channels 3 Reimar Spohr a, b, c*, Cristian Zet d, Bernd Eberhard Fischer b, Helge Kiesewetter b, Pavel Apel e, Igor Gunko f, 4 g b Takeshi Ohgai , Lars Westerberg 5 6 a 7 Department of Physics and Materials Science, Uppsala University, Box 530, 75121 Uppsala (Sweden) b 8 GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt (Germany) 9 c Applied Physics, Universität Frankfurt, Max-von-Laue-Str. 1, 60438 Frankfurt (Germany 10 d Technical University "Ghe Asachi", Bd. D. Mangeron 53, 700050 Iasi (Romania) 11 e Joint Institute for Nuclear Research (JINR), 141980 Dubna (Russia), 12 f RD&G, Grundstr. 27, 64289 Darmstadt (Germany) 13 g 14 Nagasaki University, Bunkyo-Machi 1-14, Nagasaki 852-8521 (Japan) 15 * e-mail address of responding author: [email protected] 16 17 18 19 Abstract 20 We describe a system for fabricating prescribed numbers of ion track nanochannels and nanowires 21 from a few hundred down to one. It consists of two parts: First, a mobile TAPE TRANSPORT SYSTEM, 22 which, in connection with an ion beam from a heavy-ion accelerator (nuclear charge Z above 18 and 23 24 specific energy between 1 and 10 MeV/nucleon) tuned down to low flux density by means of defocusing 25 and a set of sensitive fluorescence screens, can fabricate a series of equidistant irradiation spots on a tape, 26 whereby each spot corresponds to a preset number of ion tracks. The tape transport system uses films of 27 28 36 mm width and thicknesses between 5 and 100 µm. The aiming precision the system depends on the 29 diameter of the installed beam defining aperture, which is between 50 and 500 µm. The distance between 30 neighboring irradiation spots on the tape is variable and typically set to 25 mm. After reaching the preset 31 number of ion counts the irradiation is terminated, the tape is marked and moved to the next position. The 32 33 irradiated frames are punched out to circular membranes with the irradiation spot in the center. The 34 second part of the setup is a compact CONDUCTOMETRIC SYSTEM with 10 picoampere resolution 35 consisting of a computer controlled conductometric cell, sealing the membrane hermetically between two 36 37 chemically inert half-chambers containing electrodes and filling/flushing openings, and is encased by an 38 electrical shield and a thermal insulation. The ion tracks can be etched to a preset diameter and the system 39 can be programmed to electroreplicate nanochannels in a prescribed sequence of magnetic/nonmagnetic 40 metals, alloys or semiconductors. The goal of our article is to make the scientific community aware of the 41 42 special features of single ion fabrication and to demonstrate convincingly the significance of controlled 43 etching and electroreplication. 44 Keywords: conductometry, conductometric cell, electrodeposition, micro and nanofabrication, 45 GMR, ion track technology, magnetoelectronics, nanowires, phase detection, real-time control, self- 46 47 organization, sensor-technology, single-ion, spintronics, surfactant. 48 PACS 2010 Codes 49 81.07.-b Nanoscale materials and structures: fabrication and characterization 50 51 81.07.Gf Nanowires 52 81.15.Pq Electrodeposition, electroplating 53 81.16.-c Methods of micro- and nanofabrication and processing 54 81.20.-n Methods of materials synthesis and materials processing 55 56 85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated 57 magnetic field 58 59 60 61 62 63 64 65 Controlled fabrication of … 2 9-Dec-09 Contents 1 2 1. Introduction 2 3 1.1. Ion track technology 2 4 5 1.2. Single ion techniques 3 6 1.3. From random to deterministic 3 7 1.4. Alternative techniques 4 8 9 1.5. Goal of this report 4 10 11 2. Piercing polymer foils with a preset number of ions 5 12 2.1. Ion beam requirements 5 13 2.2. Tape transport system 5 14 15 2.3. Low flux beam diagnostics 6 16 2.4. Performing an irradiation 7 17 2.5. Digital control system 8 18 19 2.6. User interface 8 20 21 3. Single ion track etching and replication 8 22 3.1. Conductometric system 8 23 3.2. Track replication 9 24 25 3.3. Computer interface 9 26 3.4. User interface 10 27 28 4. Single-ion track applications 10 29 4.1. Etching of single track 10 30 31 4.2. Etching of 100 tracks 11 32 4.3. Probability of double tracks 12 33 4.4. Modifying cone angle 12 34 35 4.5. Asymmetric single pores 13 36 4.6. Surfactant assisted etching 13 37 4.7. Magnetoresistance of homogeneous wires 14 38 39 4.8. Magnetoresistance of layered wires 15 40 4.9. Relevance of resistance for magnetic sensors 15 41 42 5. Conclusions and Outlook 16 43 44 6. Acknowledgement 16 45 46 References 17 47 48 49 50 1. Introduction 51 52 1.1. Ion track technology 53 Ion tracks are the result of the passage of swift heavy ions through solid matter and can be etched 54 selectively in many– preferentially homogeneous and insulating – materials resulting in cones or 55 56 channels. The smallest dimension corresponds to the size of the activated zone, which is between 6 and 57 20 nm and depends on the radiation sensitivity of the material. The smoothness of the etched track wall 58 depends on the homogeneity of the used material which is related with its optical transparency. The range 59 of materials which can be etched selectively after ion irradiation comprises minerals, glasses and many 60 61 62 63 64 65 Controlled fabrication of … 3 9-Dec-09 transparent polymers, among which polycarbonate (PC) and allyl diglycol carbonate (CR-391) are most 1 widely used. A survey of materials is provided in the classical book by Fleischer, Price, and Walker [1]. 2 Track studies with lengths between 1 and 100 µm are common, usually based on ions heavier than argon 3 4 in a specific energy range between 1 and 10 MeV/nucleon. For relativistic ions even track lengths up to 5 700 µm have been observed [2]. 6 7 1.2. Single ion techniques 8 Ion tracks were discovered by D.A. Young in 1957 [3]. Their technological potential was soon 9 10 recognized by Fleischer, Price and Walker [4] who applied the technique for fabricating homoporous 11 biological filter materials [5] which stimulated branching-out research activities in many fields [1]. 12 DeBlois and Bean [6] and Possin [7] performed the first experiments with single ion tracks. They selected 13 single etched channels in thin pieces of muscovite mica containing few natural fission fragment tracks per 14 15 sample. Artificial ion tracks became possible at cyclotrons [8-11] and linear accelerators [12]. The 16 technique of single track irradiation was first developed at GSI where the combination of rapid beam 17 switching with single ion detection opened the possibility to fabricate single track membranes predictably 18 19 [13-16], starting with an aperture for a red cell deformability sensor (Fig 1, center) [17]. As the exact 20 location of the ion track is uncritical for this sensor, a small circular aperture of 50 µm diameter was used 21 to place the ion on the polymer foil. For still smaller apertures slit scattering becomes rapidly dominant, 22 increasing with 1/r, where r is the aperture radius. Independently, at GSI an ion microbeam was 23 24 developed [18], capable of placing individual ions with a precision of 1.3 µm and demonstrated with a 25 mass production of a regular pattern [19]. 26 Individual nanochannels and nanowires resulting from single track irradiations have been used in a 27 28 variety of fields, e.g. as weak links between adjacent superfluid volumes [20-21], as pH-sensitive, current 29 rectifying, asymmetric apertures [22-23], and as Giant Magnetic Resistance based magnetic field sensors 30 [24-27]. 31 32 33 34 35 36 37 38 39 40 41 42 43 Fig 1 Random, single-ion, and microbeam2 irradiation. 44 45 1.3. From random to deterministic 46 47 The irradiation technique depends on the required spatial distribution of the ion tracks. Usually ion 48 tracks are distributed at random. Random tracks are used to study and modify global properties. 49 Randomness can be an advantage or a disadvantage, depending on the application. In filter applications 50 the problem of multipore configurations exists and is tackled by wide angle irradiations. Fig 1 (left) 51 52 shows a random distribution of about 100 etched cones of 32 µm diameter in glass. At the given nominal 53 porosity P 0.12 (defined as the product of fluence F and area A of an individual etched track, where F is 54 the number of ions impinging per unit area), about 14 double and 1 triple track configurations were 55 56 formed. Fig 1 center shows an etched channel of 4 µm diameter, fabricated for red blood cell 57 deformability studies.